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CONTROL OF VIRUS DISEASES

The only spray treatment likely to be needed for the control of virus diseases is that designed to keep down insects, for these are the virus carriers. Burn plants with suspected virus symptoms to eliminate sources of infective material. Infected plants will not recover, and it is useless trying to save them. Support this destruction — especially in greenhouses — by regular spraying or fumigation to keep down insects. Annuals, which are, of course, propagated by seed, in general keep free of virus infection.

Take cuttings from healthy plants only, and wipe or dip the knife used to prepare them in disinfectant. When propagating plants such as strawberries select runners from healthy and vigorous plants.

CORRECTION OF NON-PARASITIC DISORDERS

Non-parasitic troubles, such as hail damage, can hardly be avoided, but the provision of some kind of protective cover can save serious frost damage being done to some crops. Imperfections in the soil, such as acidity, excessive alkalinity or faulty drainage can usually be corrected in the long run and so, too, can food deficiencies if these are correctly diagnosed.

It is important to see that some plants get all the necessary food elements. If fruit trees, for example, are allowed to suffer from malnutrition during the growing period, the resulting fruit, when stored, may show signs of internal break-down (browning) long before it is ripe.

NOTIFIABLE DISEASES

There are certain diseases, known as ‘notifiable diseases’, which must be reported to the Ministry of Agriculture, Fisheries and Food’s Plant Pathology Laboratory at Harpenden, Hertfordshire, as soon as they arise. (A list can be obtained either from the Ministry or from the local County Agricultural Advisory Service.) An example is potato wart. There are various regulations about the selling of diseased plants and restrictions are imposed on the importation of plants from abroad. The intention, of course, is to protect stocks of plants in this country from infection by dangerous diseases.

The movement of plants between nurseries and gardens in this country cannot be regulated easily, but voluntary schemes are available for growers and nurserymen to encourage them to raise and sell clean stocks. The best known is probably the Scottish seed potato certification scheme. The grower has his stocks rigorously inspected during the growing season and, if all is well, he is granted a certificate which indicates that the stock is true to type and free from virus infection. Encouragement is thus given to the purchase of certified fresh Scottish potato seed, and the crippling effect of virus and the lower crop yield which is often obtained from home-saved seed is avoided.

There are similar voluntary schemes for plants such as strawberries, raspberries and even shallots. Varieties of those plants covered by such schemes and certified free from virus infection are available.